On my 200k R-12 ride last month, I started in a 40 degree rain at 06:30. My first flat was before I left the parking lot, when I ran over a carton staple. The second flat was about 8 miles into the ride, and the valve core shot out and stuck in my right calf like a dart. The third flat was less than 2 miles later from a sliver of car-accident remnants.
Yep, 3 flats in less than 10 miles. Dark and raining the entire time. At least it was 40 degrees, and not 19. I would have called it quits if that happened in 19 degree weather.